Bolt fastening method and apparatus

Abstract

A bolt is fastened up to a predetermined snug torque Ts and then the bolt is further fastened by a specified angle θt from a bolt angle corresponding to the snug torque Ts. Herein, in order to obtain excess and deficiency of the fastening angle up to the snug torque Ts, an angle-variation difference between the fastening angle θsb of the bolt at the point where the fastening torque of the bolt has reached the snug torque Ts and a standard angle θsa of the snug torque Ts is calculated. And, addition of this angle-variation difference to a base angle is set as the new specified angle θt to correct the excess and deficiency. Accordingly, variation in a fastening shaft force can be restrained even if the snug torque is set at a relatively high torque in the bolt fastening method using the torque+angle method.

Description

BACKGROUND OF THE INVENTION[0001]The present invention relates to a bolt fastening method and apparatus.[0002]A bolt fastening method (torque method) in which the bolt fastening management is conducted by utilizing the proportional relationship between the fastening torque T and the fastening shaft force (in the bolt elasticity area) is known. While this torque method is superior in work efficiency, there may occur a large variation in the fastening shaft force according to the coefficient of friction between the screw face and the seat face of the bolt (see FIG. 11). Accordingly, another bolt fastening method (torque+angle method), which is shown in US Patent Application Publication No. 2006 / 0218768, has been used, in which the bolt is fastened up to the predetermined snug torque Ts (a fastening torque at a start point for an effective and substantial fastening) and then the bolt is further rotated (fastened) by a specified angle θk from the standard bolt angle corresponding to the...

AI Technical Summary

Benefits of technology

[0004]The present invention has been devised in view of the above-described matters, and an object of the present invention is to provide a bolt fastening method which can properly restrain the variation in the fastening shaft force even if the snug torque is set at a relatively high torque in the torque+angle method. Another object of the present invention is to provide a bolt fastening apparatus which uses the above-described bolt fastening method.

[0006]According to the present invention, the specified angle for the bolt to be further fastened from the bolt angle corresponding to the snug torque is properly corrected (updated), so that the final fastening shaft force of the bolt can be made uniform. Thereby, the variation in the fastening shaft force can be restrained properly even if the snug torque is set at the relatively high torque.

[0007]According to an embodiment of the first aspect of the present invention, one of a plurality bolts to be fastened is selected as a standard bolt, and the obtained fastening angle of the standard bolt at the point where the fastening torque of the bolt has reached the snug torque from the fastening-angle start standard point is used as the standard angle of the snug torque. Thereby, the fastening shaft force of the other bolt than the standard bolt can be made approximate the fastening shaft force of the standard bolt easily, and the fastening shaft forces of all of the bolts can be made uniform.

[0008]According to another embodiment of the first aspect of the present invention, the obtaining of the fastening angle of the bolt at the point where the fastening torque of the bolt has reached the snug torque from the fastening-angle start standard point is conducted for a plurality bolts to be fastened, an average angle of the obtained fastening angles of the plurality of bolts is obtained, and the average angle is used as the standard angle of the snug torque. Thereby, the correction of the fastening shaft force of the bolts can be properly achieved regardless of presence of the plural bolts to be fastened, so that the fastening shaft forces of the plural bolts can be made uniform.

[0009]According to another embodiment of the first aspect of the present invention, the plurality of bolts for obtaining the average angle are part of bolts which are selected from all of the bolts to be fastened. Thereby, even if there are many bolts, the average angle are easily obtained, and the correction is made based on the average angle, thereby making the fastening shaft forces of the plural bolts uniform. Further, the fastening angle of the specified bolt which is largely different from the one of the other bolt(s) may be excluded from averaging, so that more appropriate average angle can be used to provide the proper fastening, considering the situation of an object product to be fastened with the bolts.

[0010]According to another embodiment of the first aspect of the present invention, the selected plural bolts are fastened substantially at the same time, respective fastening angles of the bolts at the points where the fastening torques of the bolts have reached the snug torques from the fastening-angle start standard points are obtained, and the average angle is obtained from the respective fastening angles obtained. Thereby, the fastening shaft forces of the plural bolts can be made uniform, achieving the efficient fastening step of the bolts

Problems solved by technology

In the above-described bolt fastening method (torque+angle method), however, there may occur the variation in the fastening shaft force according to the coefficient of friction (between the screw face and the seat face) in the fastening area before reaching the snug torque Ts, which may improperly affect the fastening shaft force F of the fastening after the fastening point of the snug torque Ts (see FIG. 12).

In this case, while it may be considered to set the snug torque Ts at a very low torque for the purpose of restraining the variation of the fastening shaft force (fastening angle) at the snug torque Ts, there occurs necessity to cope with restrictions of fastening conditions (for example, there is a problem in that it may be recognized by mistake to have reached the snug torque due to dusts being stuck or the like).

Thereby, the above-described setting would not be sufficient.

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